WO 2006/042298 describes a photo-mechanical hearing aid, wherein the tympanic membrane is activated by mechanical vibration signals, which are generated by a transducer in response to optical signals received by the transducer. The transducer is attached to the tympanic membrane. The transducer is therefore not mechanically coupled to the generator producing the optical signals and can therefore stimulate the tympanic membrane or, alternatively, a bone in the ossicular chain, an external portion of the cochlea, or a portion elsewhere between the tympanic membrane and the cochlea in the hearing transduction pathway by mechanical vibration signals without interference from mechanical coupling to an outside component.
U.S. Pat. No. 6,537,200 B2 describes a hearing system for implantation of its transducer section into the auditory canal. For transmission of auditory signals, mechanical transducer vibrations are mechanically transported by a coupling element that is coupled to an ossicle of the ossicular chain, from which they can cause a corresponding hearing impression along the natural pathway.
U.S. Pat. No. 6,137,889 describes a hearing aid that transmits vibrations via a vibrationally conductive assembly to the tympanic membrane. The vibrationally conductive assembly comprises a tympanic coupling element, e.g. a coupling pad, which is placed on the tympanic membrane for transmission of the mechanical vibrations.
In the intact ear, sound pressure waves from the environment travel through the external auditory canal, are then transmitted through the ear drum and middle ear ossicles to the fluid within the cochlea. The fluid movement within the cochlea induces the depolarization of the sensory epithelium formed by hair cells. This depolarisation is transformed into nervous signals which are transmitted from the base of the hair cells to the dendrites of the spiral ganglion, which is the first neuron on the auditory pathway, and from the spiral ganglion further to the central auditory system, and finally reaching the auditory cortex to elicit a sound perception. The nervous signals which are transmitted via the spiral ganglion cells to the central auditory system can be recorded as auditory brainstem responses (ABR).